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thought that the lander landed
awkwardly and hit a boulder, and
the very low gravity of the comet
meant Philae bounced right off
again. It was later calculated that
Philae bounced up about 3,000 ft
(1 km) from the surface before falling
back again, tumbling to a resting
place on the edge of the target
landing zone. Unfortunately, the
lander ended up in the shadow of a
cliff and appeared to be at an angle.
Without sunlight to recharge its
batteries, Philae had only about
48 hours of power to perform its
primary science missions, returning
data on the chemical composition
of the dust and ice, and performing
scans with the CONSERT
instrument on Rosetta. A last-ditch
plan to push the lander out into the
sunlight using the harpoons (which
had not fired on landing) failed, and
Philae shut down into safe mode.
Approaching the sun
Despite this setback, the
perilous Philae landing was
deemed a success. The hope
was that Philae’s shaded location
would become sunnier as the
comet approached the sun.
The comet would reach its
perihelion, or closest point, in
August 2015. On the approach,
comet 67P began to heat up and
its surface erupted with jets of dust
and plasma. Rosetta was sent on
a complex orbital path so that it
could fly low over the comet and
pass through the denser regions
of the coma, or cloud of material,
that was forming around 67P.
Its path also took it farther out,
providing a more complete picture
of the ways in which the comet
was changing as it entered the
warmer part of the solar system.
In mid-June 2015, Philae received
enough sunlight to wake up, and
began intermittent communication
with Rosetta, allowing further
CONSERT scans. In early July,
however, it fell silent again.
Fortunately, it was spotted by the
OSIRIS camera on September 2,
2016, as it approached within
1.7 miles (2.7 km) of the comet.
Knowing Philae’s precise landing
spot allows scientists to place the
information it sent back a year
earlier into context.
After comet 67P passed
perihelion in August 2015, the
solar power available to Rosetta fell
rapidly. In September 2016, Rosetta
was instructed to get slowly nearer
to the comet. It ended its mission onTHE TRIUMPH OF TECHNOLOGY
September 30 by making a controlled
crash-landing, returning data right
up to the moment of impact.Alien water
The amount of deuterium (“heavy
hydrogen”) found in 67P’s water
is much greater than in the water
found on Earth, evidence against
the idea that Earth’s water is of
extraterrestrial origin. The mission
has found many carbon-based
compounds, but only one amino acid
(the building block of proteins) and
no nucleic acids (the ingredient of
DNA) have been detected in the data.
Rosetta’s results will allow
astronomers to better understand
comets and whether 67P is a typical
body. Combined with discoveries
from the Kuiper belt, this is hoped
to reveal what the solar system was
made of as the sun formed. ■On July 16, 2016, Rosetta was just
8 miles (12.8 km) from the center of
comet 67P. This image covers an area
about 1,500 ft (450 m) across. It shows
a dust-covered rocky surface.